Lactase non-persistence (adult-type hypolactasia) results in digestive system malabsorption of lactose, the carbohydrate macronutrient present in milk. Human DNA sequence variants associated with intestinal lactase persistence and non-persistence have recently been identified. This research project focuses on characterization of the genetic determinants of intestinal lactase persistence in humans. We have previously characterized molecular mechanisms regulating intestine-specific expression of the rat lactase gene in cell culture and in living animals. We will now direct attention to characterization of the molecular mechanisms mediating human lactase gene persistence and non- persistence and the temporal decline of lactase in rodents. Preliminary studies have shown that DNA sequences in the region of lactase gene polymorphisms can bind nuclear proteins and enhance lactase promoter activity. We hypothesize that DNA polymorphisms associated with lactase persistence function to regulate lactase gene transcription in adult human enterocytes via differential interaction with specific nuclear protein transcription factors. Research objectives are therefore aimed at defining the mechanistic roles of genetic determinants of human lactase persistence. In Aim 1, we will characterize a functional role for DNA polymorphisms associated with persistence of lactase gene transcription in humans. Functional characterization of lactase gene polymorphisms will be investigated in cell culture and in vivo in transgenic mice. In Aim 2, we will define the molecular mechanisms regulating human lactase persistence gene transcription. The goals of this aim will be to identify and characterize nuclear proteins capable of interacting with DNA sequences in the region of lactase gene polymorphisms associated with lactase persistence and to characterize whether the nuclear proteins function to regulate lactase transcription. In Aim 3, to complement our investigation of the mechanism of lactase persistence in humans, we will further elucidate mechanisms regulating the temporal decline of lactase in rodents. Knowledge of mechanisms regulating human lactase gene expression may provide future novel diagnostic, therapeutic or prognostic strategies for gastrointestinal disorders that result in loss or inappropriate gain of epithelial cell digestive function. Our combination of in vitro and in vivo experimental approaches will elucidate roles for the genetic determinants associated with lactase persistence and non-persistence.